linux-kernel - [PATCH 3/4] x86/mtrr: Add a prepare_set hook to mtrr

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Message-ID: <20260121141106.755458-4-jgross@suse.com>
Date: Wed, 21 Jan 2026 15:11:05 +0100
From: Juergen Gross <jgross@...e.com>
To: linux-kernel@...r.kernel.org,
	x86@...nel.org
Cc: Juergen Gross <jgross@...e.com>,
	Thomas Gleixner <tglx@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 3/4] x86/mtrr: Add a prepare_set hook to mtrr_ops

In order to prepare dropping the cache_disable_lock add a new hook
to struct mtrr_ops, allowing to set some global state before calling
the .set hook on all active CPUs.

Move setting of mtrr_state.var_ranges[] from generic_set_mtrr() to
the new prepare hook. Note that doing that only once outside the
cache_disable_lock is fine, as generic_set_mtrr() is called via
set_mtrr() only and this call is protected by mtrr_mutex.

Signed-off-by: Juergen Gross <jgross@...e.com>
---
 arch/x86/kernel/cpu/mtrr/generic.c | 32 ++++++++++++++++++++++++------
 arch/x86/kernel/cpu/mtrr/mtrr.c    |  3 +++
 arch/x86/kernel/cpu/mtrr/mtrr.h    |  2 ++
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index ac95b19b01d0..bfd5a7ba17cb 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -1057,6 +1057,31 @@ void mtrr_generic_set_state(void)
 	cache_enable(&state);
 }
 
+/**
+ * generic_prepare_set_mtrr - set variable MTRR register data in mtrr_state
+ *
+ * @reg: The register to set.
+ * @base: The base address of the region.
+ * @size: The size of the region. If this is 0 the region is disabled.
+ * @type: The type of the region.
+ *
+ * Returns nothing.
+ */
+static void generic_prepare_set_mtrr(unsigned int reg, unsigned long base,
+				     unsigned long size, mtrr_type type)
+{
+	struct mtrr_var_range *vr = &mtrr_state.var_ranges[reg];
+
+	if (size == 0) {
+		memset(vr, 0, sizeof(struct mtrr_var_range));
+	} else {
+		vr->base_lo = base << PAGE_SHIFT | type;
+		vr->base_hi = (base >> (32 - PAGE_SHIFT)) & ~phys_hi_rsvd;
+		vr->mask_lo = -size << PAGE_SHIFT | MTRR_PHYSMASK_V;
+		vr->mask_hi = (-size >> (32 - PAGE_SHIFT)) & ~phys_hi_rsvd;
+	}
+}
+
 /**
  * generic_set_mtrr - set variable MTRR register on the local CPU.
  *
@@ -1085,13 +1110,7 @@ static void generic_set_mtrr(unsigned int reg, unsigned long base,
 		 * clear the relevant mask register to disable a range.
 		 */
 		mtrr_wrmsr(MTRRphysMask_MSR(reg), 0, 0);
-		memset(vr, 0, sizeof(struct mtrr_var_range));
 	} else {
-		vr->base_lo = base << PAGE_SHIFT | type;
-		vr->base_hi = (base >> (32 - PAGE_SHIFT)) & ~phys_hi_rsvd;
-		vr->mask_lo = -size << PAGE_SHIFT | MTRR_PHYSMASK_V;
-		vr->mask_hi = (-size >> (32 - PAGE_SHIFT)) & ~phys_hi_rsvd;
-
 		mtrr_wrmsr(MTRRphysBase_MSR(reg), vr->base_lo, vr->base_hi);
 		mtrr_wrmsr(MTRRphysMask_MSR(reg), vr->mask_lo, vr->mask_hi);
 	}
@@ -1156,6 +1175,7 @@ int positive_have_wrcomb(void)
 const struct mtrr_ops generic_mtrr_ops = {
 	.get			= generic_get_mtrr,
 	.get_free_region	= generic_get_free_region,
+	.prepare_set		= generic_prepare_set_mtrr,
 	.set			= generic_set_mtrr,
 	.validate_add_page	= generic_validate_add_page,
 	.have_wrcomb		= generic_have_wrcomb,
diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
index 4b3d492afe17..32948fb4e742 100644
--- a/arch/x86/kernel/cpu/mtrr/mtrr.c
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
@@ -175,6 +175,9 @@ static void set_mtrr(unsigned int reg, unsigned long base, unsigned long size,
 				      .smp_type = type
 				    };
 
+	if (mtrr_if->prepare_set)
+		mtrr_if->prepare_set(reg, base, size, type);
+
 	stop_machine_cpuslocked(mtrr_rendezvous_handler, &data, cpu_online_mask);
 
 	generic_rebuild_map();
diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.h b/arch/x86/kernel/cpu/mtrr/mtrr.h
index 2de3bd2f95d1..4d32c095cfc5 100644
--- a/arch/x86/kernel/cpu/mtrr/mtrr.h
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.h
@@ -17,6 +17,8 @@ extern unsigned int mtrr_usage_table[MTRR_MAX_VAR_RANGES];
 
 struct mtrr_ops {
 	u32	var_regs;
+	void	(*prepare_set)(unsigned int reg, unsigned long base,
+			       unsigned long size, mtrr_type type);
 	void	(*set)(unsigned int reg, unsigned long base,
 		       unsigned long size, mtrr_type type);
 	void	(*get)(unsigned int reg, unsigned long *base,
-- 
2.52.0